Traditional high intensity resistance exercise programs have been shown to have positive effects on bone metabolism. KAATSU resistance training, which combines low intensity resistance exercise with vascular restriction, accelerates muscle hypertrophy, however, the benefits of this type of training on bone have not been established. PURPOSE: To investigate the effects of acute (1 bout) KAATSU training for knee extensors and knee flexors on serum bone biomarkers in young men, 18-30 years of age. METHODS: Nine males performed two test sessions, KAATSU (vascular restriction + low intensity resistance exercise) and control (low intensity resistance exercise only) 48 hours apart in random order. The exercise protocol consisted of 1 set of 30 reps followed by 3 sets of 15 reps with 30 seconds rest between sets at 20% 1-RM for both muscle groups. On both days, fasting blood draws were obtained immediately prior to exercise, immediately post exercise and 30 minutes post exercise for the measurement of the bone formation (bone-specific alkaline phosphatase, BAP) and bone resorption (cross-linked N-telopeptide of type I collagen, NTx) markers. Hematocrit was measured at each sample time to estimate plasma volume changes. Serum samples were aliquoted and frozen at -70°C until the BAP (Metra BAP EIA kit, Quidel Corporation) and NTx (Osteomark® NTx Serum, Wampole Laboratories) assays were performed. RESULTS: KAATSU training resulted in greater plasma volume decreases (p<.05) immediate post exercise compared to the control session. There was a significant (p<.05) training x time effect for NTx levels. 30 minute post exercise NTx levels (21.4±3.4 nM BCE) significantly (p<.05) decreased from baseline (24.9±4.3 nM BCE) after KAATSU training but not in response to the control training. After correcting for plasma volume shifts, significant decreases in serum NTx were observed for both KAATSU post exercise samples. There were no significant (p>.05) training or time effects for BAP. CONCLUSION: A single bout of KAATSU trining resulted in decreases in the bone resorption marker (NTx) but had no effect on the bone formation marker (BAP). The NTx response to KAATSU was not mediated by shifts in plasma volume.

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Low-intensity resistance exercise combined with blood flow restriction has been shown to elicit hormonal and neuromuscular responses similar to those with high-intensity resistance exercise. However, muscle fatigue characteristics during resistance exercise with restricted blood flow have not been clarified. Therefore, we measured maximal voluntary torque values during isokinetic concentric leg extensions across 30 repetitions at 180°/s either with blood flow restriction (BFR) or without restriction (CON) in eight healthy adults. The exercise was performed at the rate of either 30 repetitions/minute (BFR30 and CON30) or 15 repetitions/minute (BFR15 and CON15) designed to allow different rest intervals between contractions. Muscle fatigue was quantified by two methods: slope of peak isokinetic torque values through the 30th repetition and percent decrease in force from the first 5 repetitions to the last 5 repetitions. At the rate of 30 repetitions/minute, both fatigue rates were similar between BFR and control group. On the contrary, both fatigue rates were significantly higher in BFR15 group than the CON15 group (p<0.05). The results indicate that during resistance exercise performed with longer inter-repetition rest intervals, blood flow restriction is more effective at inducing muscle fatigue and thus may increase the training response. Furthermore, inter-repetition rest intervals of less than 3.5 seconds can increase fatigue level regardless of muscle perfusion.

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